Some portable devices comprise integrated speakers for creating sound such as playing back music or having a telephone conversation. The loudness and bandwidth of the integrated speakers are important especially in environments where the ambient noise levels are high, even indoors. The loudness of the integrated speakers in a portable device is important for perception of ringtones of a mobile telephone. In some countries the loudness of the integrated speakers is important for listening to FM radio broadcasts.
In some parts of the world a portable device with an integrated speaker may be the only device the user owns which is capable of playing music. For example, a user may only be able to play music using a loudspeaker of a mobile telephone. The loudness and bandwidth of sound from an integrated speaker are even more important if a user is solely reliant on an integrated speaker of a portable device for music playback.
It is known to increase the loudness of integrated speakers by actively amplifying sound by electronic solutions. For example, circuitry comprising large transducers, components for signal processing and other electrical modifications has been used. Other solutions further comprise external loudspeakers. It is also common to use two speakers where their output is acoustically coupled, for example by mutual acoustic coupling, to increase the loudness. In addition, these known solutions can also improve bandwidth expansion. For example, an integrated speaker can operate in a slightly lower frequency region than its normal operation range. Typically digital signal processing (DSP) may increase loudness and/or improve bandwidth by using one or more of the following: digital gains, equalization (EQ), single or multiple dynamic range controllers (DRC) and transducer protection comprising displacement and temperature controller to prevent distortion. It is understood that there may be more additional systems or algorithms which are designed for use in digital signal processing. For example, in addition there may be and/or other systems in a playback chain such as electrical filters. Disadvantageously, the additional components are expensive and use additional power which can reduce portable device operating time dramatically.
Another technique for increasing the loudness and bandwidth of an integrated speaker is using an external accessory. One such accessory is a desk stand or a cradle for a hands free car kit which provides passive amplification for a portable device. However, external accessories providing either active or passive amplification are expensive and bulky. This means the user cannot easily transport the desk stand and has to keep it in one place. Furthermore manufacture of such external accessories is complex and requires an expensive manufacturing set up and equipment.